1. Field of the Invention
The present invention relates to radiation surface-curable room temperature vulcanizing (RTV) silicone compositions, and to a method of making and using same.
2. Description of the Related Art
RTV silicone materials are widely used in industry as well as in consumer markets as sealants, adhesives, coating, potting compounds, etc. Typically, these materials are manufactured by endcapping, .alpha.,.omega.-silanol terminated silicones with various crosslinkers such as alkoxysilanes, oximinosilanes, acetoxysilanes, aminosilanes, and other silanes with hydrolyzable groups attached to the silicon atom(s) thereof.
The resulting RTV silicone materials are stored in moisture impermeable containers. During application, the materials are extruded or otherwise applied and exposed to ambient conditions for curing. The moisture in the air then will hydrolyze the hydrolyzable groups (alkoxy, oximino, acetoxy, amino, etc.) on the silicon atom(s), to form silanol, either with or without the assistance of an added catalyst.
The resulting silanol can then further react with remaining unhydrolyzed groups in a condensation reaction, to form a siloxane linkage resulting in the cure of the silicone material.
The above-discussed reactions are illustrated below: ##STR1## where R.dbd.alkyl, aryl etc., X.dbd.OR, oximino, acetoxy, amino, amido etc., and n=0-2.
Depending on the X group, the above reaction may or may not require the assistance of a catalyst. ##STR2##
Again, depending on X group, catalyst(s) may or may not be present. ##STR3## Although the RTV materials are very reliable and possess superior properties in the aforementioned end use applications (sealants, adhesives, coatings, potting compounds, etc.), the RTV materials often are very slow to cure. For example, a typical RTV silicone formulation often requires overnight curing before acceptable cure properties for the intended end use applications can be fully realized.
As a result, there exists a need to "fix," i.e., spatially immobilize, the applied RTV quickly, so that the applied material will not migrate from the locus of intended use, before a full cure of the RTV silicone is achieved. Such migration may be extremely deleterious. For example, if a sealant RTV formulation is applied to a joint to effect waterproof sealing thereof, migration such as sag or running of the sealant can take place (in the absence of adequate curing of the formulation). The migrated sealant formulation as a result may no longer overlie the joint to be sealed, so that the appertaining jointed structure may be rendered deficient or even useless for its intended purpose.
U.S. Pat. No. 4,526,955 to Bennington et al. describes radiation-polymerizable compositions including organopolysiloxanes having --N--Si or N--O--Si linkages.
Japanese Patent Application No. 4-69901 filed Feb. 12, 1992 by Three-Bond Co., Ltd. discloses an ultraviolet-curing, addition-polymerization-type silicone composition which is curable at room temperature. The disclosed silicone composition comprises a polydiorganosiloxane containing vinyl groups and a polydiorganosilane in which at least 4 silicon atoms are directly bonded in the formula R.sub.5 (Si(R.sub.3)(R.sub.4)).sub.n R.sub.6 in which R.sub.3 -R.sub.6 are alkyl or aryl, and n is 4 or greater, with the proviso that R.sub.5 and R.sub.6 may be directly bonded to one another. An addition polymerization catalyst is also included in the composition, such as a platinum catalyst. The composition is uv-light curable with the occurrence of radical addition polymerization.
Hoffman, V., et al., J. Mol. Struct., 293, 253-256 (1993) describes oligomers including a vinyl group-containing dimethylsiloxane which are thermally as well as photochemically crosslinkable.
Roth, W., et al., Adv. Mater., 2(10), 497-498 (1990) discloses a methylvinyl-dimethylsiloxane composition that is devoid of photoinitiators, and undergoes radical crosslinking when exposed to laser radiation.
Barrall, E., et al., J. Polym. Sci., Polym. Symp., 71, 189-202 (1984) describes uv-cured polydimethylsiloxanes containing pendant vinyl groups, wherein the curing involves dicumyl peroxide-mediated vulcanization.
U.S. Pat. No. 4,064,027 to Gant describes a uv-curable composition consisting essentially of a vinyl-containing siloxane and siloxane-containing, silicon-bonded hydrogen atoms, in which a mercaptofunctional silicone may be employed as a cure accelerator.
U.S. Pat. No. 4,742,092 to Inoue et al. and U.S. Pat. No. 4,595,471 to Preiner et al. show UV and dual UV/moisture curable silocones which employ photocurable (meth)acryloxy and isopropenyloxy group containing silicones in combination with mercapto-containing silicones.
Ep 0492828 discloses UV curable silicones of alkoxy terminated polydiorganosiloxanes in combination with an alkoxy silicone compound which is capable of photo reactivity. This patent, however, teaches compositions wherein the silanol terminated diorganopolysiloxane is first reacted with solely hydrolyzable groups containing endcappers. As a result, the silicones are not terminated with UV activatable groups.
Accordingly, it would be a substantial advance in the art, and is correspondingly an object of the present invention, to provide an RTV silicone composition which is rapidly "settable" at the application locus following application of the formulation to such locus, so that migration effects (sag, non-bonding, loss of joint seal integrity, exposure of components intended to be encapsulated, etc.) are minimized or eliminated, but is curable in a conventional manner under ambient atmosphere exposure conditions to moisture cure and achieve superior fully cured properties.
Another object of the present invention is to provide an improved RTV silicone composition of such character, which is readily formulated in a convenient manner using conventionally available resin and formulation components.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.